Deforming a modified Mesh to Match a sculpted Mesh with an extra Subdivision applied
Shrink Wrap Modifier  

Hi Blazer, sounds like you have a good workflow going for your project, and it sounds like you're currently looking for the shrink wrap modifier. You can add the shrink wrap modifier to the lower res object, and then in the target field, add the name of the multires object. Before you add the shrinkwrap modifier, you may also want to put both objects in the same xyz space on different layers, and enable the xray option on the lower res object. In a sculpting/retopology/baking workflow, the shrinkwrap modifier is great tool.